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Syntax

RELEASE_LOCK(str)

Description

Releases the lock named by the string str that was obtained with GET_LOCK(). Returns 1 if the lock was released, 0 if the
lock was not established by this thread (in which case the lock is not
released), and NULL if the named lock did not exist. The
lock does not exist if it was never obtained by a call to
GET_LOCK() or if it has previously been released.

MariaDB until 10.0.1

Before 10.0.2, GET_LOCK() released the existing lock, if any. Since 10.0.2 this does not happen, because multiple locks are allowed.

str is case insensitive. If str is an empty string or NULL, RELEASE_LOCK() returns NULL and does nothing.